140 Dr. T. Wright on the Cidaridse of the Oolites. 



ribbon-shaped, and nearly of a uniform breadth throughout. 

 The poriferous avenues are broad j the pores are oblong and set 

 in pairs in a single file at short distances apart. The area? are 

 flat, slightly raised, and have four rows of granules ; the external 

 rows consist of larger granules, which range regularly on the 

 margins of the arese; the internal rows consist of small, flat, 

 almost microscopic granules; there are fifteen pairs of holes 

 opposite each of the large tubercular plates. 



The interambulacral arese are formed of broad plates ; the zig- 

 zag median sutural line is very clearly defined j each column 

 contains from eight to ten primary tubercles, so that the test of 

 this Urchin supports from 80 to 100 large spines. Each plate 

 is occupied with a smooth areola slightly furrowed at its cir- 

 cumference and raised into a boss towards the centre. The sum- 

 mit of the boss is sculptured with fifteen deep crenulations; 

 from the boss arises a short cylindrical stem terminated by a 

 small hemispherical deeply perforated spinigerous tubercle, the 

 diameter of which exceeds a little that of its stem ; the margin 

 of each areola is bounded by a circle of fifteen prominent gra- 

 nules, some of which from the equator to the anal pole are raised 

 upon broader bases. There is a granular circle around each 

 areola, but from the equator to the buccal pole one row of gra- 

 nules is common to two areolae. The interareolar spaces are 

 covered with small close-set granules of two different sizes. The 

 mouth is large, and is half the diameter of the test at the equator. 

 In the specimen before me the five strong pyramids of the lan- 

 tern are armed with conical triangular teeth in situ. The anal 

 disc was broken in all the specimens hitherto found. 



The spines are never seen attached to the test, but in the same 

 bed and lying near some of these Urchins, long cylindrical slightly 

 flattened spines have been found about 1^ inch in length and 

 from 2 to 3 lines in diameter, with a crenulated base, short neck, 

 and having the surface of the flattened stem covered with short 

 sharp prickles, the points of which are directed forwards ; these 

 spines most probably belonged to C. Fowleri, as it is the only 

 Urchin found in the same bed whose test could support such 

 large spines (fig. 5 c). 



Affinities and differences. — Cidaris Fowleri resembles C. Blu- 

 menbachii in the general form and structure of the test, but it 

 differs from that well-known species in the flatness of the am- 

 bulacral area?, in the greater breadth of the poriferous avenues, 

 and in having a greater number of plates in the interambulacral 

 columns; the granulated space between the principal tubercles 

 is wider, and the granular wreath encircling the areolae is like- 

 wise composed of smaller granules. It differs from C. Parandieri, 

 Ag., in having a greater number of tubercular plates in the 



